1. Field of the Invention
This invention relates generally to comparator circuits and, more particularly, to the input stage of an operational amplifier which utilizes junction field effect transistor (JFETs) as input devices and which level shifts the drain voltage of the JFETs to drive an NPN current mirror.
2. Description of the Prior Art
Operational amplifier input stages are known which employ NPN transistors as input devices. However, in some applications, it is desirable to provide an input stage which requires lower base currents and exhibits a higher input impedance.
In another known operational amplifier input stage, P-channel MOS field effect transistors are utilized as input devices which drive the base electrodes of a common emitter PNP level shifting stage. The outut of the input stage is taken from the collector of one of the PNP level shifting transistors. The frequency response and output impedance of this circuit is limited because the current gain of the common emitter PNP level shifting stage is greater than one.